H. A. Baker — Quartzife Pebbles of ike Oldhaven Beds. 67 



forward a certain amount of evidence of the occurrence of sandstone 

 blocks in situ in the Woolwich and Reading Beds, and further 

 supported his view by referring to the definite proof furnished by the 

 cHffs of St. Marguerite, near Dieppe, where a bed of sand underlying 

 the fossiliferous Woolwich fluviatile clays contained in several 

 parts of the section blocks of a white saccharoid concretionary 

 siliceous sandstone, which often contained rolled flint-pebbles and 

 subangular flints. 



Mr. Whitaker, in the London memoir,^ expressed his agreement 

 with the conclusions of Prestwich, but experienced similar difficulty 

 in pointing to definite evidence of sarsen-stones in situ in the 

 Woolwich and Reading Beds. Now, however, the needed evidence 

 is available. Genuine sarsens have been seen in situ in Reading 

 Beds, at Long Valley Wood, near Rickmansworth,- and at Nately 

 Scures, Hants .'^ In the London area great difficulty is occasionally 

 caused in sinking through the lower part of the Woolwich and 

 Reading Series by the puddingstones and sarsen-stones, which occur 

 in lenticular masses and offer enormous resistance to the chisels. 

 The sarsen-stone is the less common, but has been met with in the 

 east and north of London."* It was encountered in the Tube Railway 

 between King's Cross and the Angel, and also at Gerrard's Cross. 

 When the Rotherhithe Tunnel was made the engineers came upon 

 a very interesting occurrence of sarsen-stone and puddingstone in 

 the Woolwich and Reading Beds. At first a fine, hard sandstone 

 was encountered, and after a considerable length of this had been 

 cut through, the sarsen began to contain small, scattered flint- 

 pebbles. These became larger and more numerous till the rock 

 finally passed into a puddingstone. It did not retain this character 

 further on ; patches only were cemented, the rest was loose, thus 

 becoming the normal pebble-bed.^ It thus appears that the 

 cemented pebble-bed or puddingstone passes laterally into cemented 

 sand or sarsen. Mr. G. Barrow states that, in addition, it may pass 

 either above or below into sarsen, for loose blocks have been found 

 in great numbers containing the junction of the two, the matrix of 

 the puddingstone and the sarsen having exactly the same composition 

 and structure. He states that such blocks are extremely numerous 

 to the west of Great Missenden. Near Cuffley, where the new line 

 of the Great Northern Railway crosses the Cuffley Brook, the 

 puddingstone has been wejl seen in situ in the Reading Beds.*^ 

 In the Woolwich area local induration of beds by silica is a common 

 phenomenon. It is quite common, for instance, for the bed of 



1 Whitaker, Geology of London (Mem. Geol. .Surv.), vol. i, 1889, p. 479. 

 " Hopkinson, Middlesex and Hertfordshire (Jub. Vol. Geol. Assoc), pt. i, 

 1909, p. 46. 

 ■^ Proc. Geol. Assoc, vol. xxii, pt. iv, 1911, p. 242. 

 * Records of London Wells (Mem. Geol. Surv.), 1913, p. 7. 

 ^ Barrow, Proc. Geol. Assoc, vol. xxx, pt. i, 1919, pp. 5-6. 

 « Proc. Geol. Assoc, vol. xxv, pt. i, 1914, pp. 77-8. 



